Extensive studies have been made for a nonaqueous electrolyte battery which performs charge and discharge by moving lithium ions between a negative electrode and a positive electrode as a high-energy density battery.
This nonaqueous electrolyte battery is expected to be used as a medium/large power supply in addition to the use as a compact electronic device power supply. The life performance and high safety are required in the application field of the medium/large power supply.
A lithium transition metal composite oxide is used as a positive electrode active material of the nonaqueous electrolyte battery. Examples of the transition metal are Co, Mn, and Ni. In recent years, extensive studies have been made for spinel type lithium manganate and an olivine type compound such as olivine type lithium iron phosphate and olivine type lithium manganese phosphate as an inexpensive and highly safe positive electrode material.
Since the olivine type compound has a low electron conductivity, it is difficult to obtain excellent charge-and-discharge performance. The lithium manganese phosphate is preferable among the olivine type compounds in consideration of the energy density and the oxidation potential of an electrolytic solution. However, since the lithium manganese phosphate has low electron and ion conductivities, it is difficult to obtain excellent charge-and-discharge performance. In particular, the lithium manganese phosphate has low charge-and-discharge performance and accordingly poor rapid charge performance.